The Cohn-Oncley purification of therapeutic proteins from blood plasma, referred to herein in general as the Cohn process or scheme, employs a series ethanol additions and pH adjustments to purify or enrich for proteins which may be used in human therapies. Commonly purified proteins include immunoglobulins, anti-hemophiliac factors and albumin. While many manufacturers of such products utilize the basic Cohn scheme, frequently established steps may be modified or additional steps are implemented to increase either the purity and/or yield for a given product. Such steps are typically proprietary for a given manufacturer.
Since the discovery that HIV could be carried and transmitted through the use of blood products, the interest and concern about the presence of such pathogenic agents in biological products derived from blood has increased. Most recently, there has been concern that CJD, Creutzfeldt-Jakob Disease, could be transmitted through the use of blood-derived products. CJD is one of the human transmissible spongiform encephalopathies (TSE), a collection of neurodegenerative diseases that are debilitating and fatal. Infectivity associated with CJD appears to be either associated with or caused by the prion protein (PrP). Although new disease carrying viruses may be generated at any time, manufacturers of blood-based products take precautions to obtain a blood product that is free of known transmissible diseases, to the extent for which these can be tested. Unfortunately, the primary test for possible TSE infectivity is a biological assay in which rodents are injected with the material of interest to see if infectivity develops. The results of such assays require nine months to a year to develop, frequently too long to hold a manufactured lot of plasma product prior to release for use.
Therefore, a method of detecting a protein associated with a pathogen suspected of carrying infectivity such as the prion or viral surface (coat) protein is important for the blood fractionation industry. A rapid, sensitive method capable of determining the removal of virus or pathogenic prion protein would provide the blood fractionation industry with a useful tool for determining what danger of infectivity exists after a particular manufacturing process step. The decrease in viral or prion protein relative to a given product associated with a manufacturing process step is referred to herein as “clearance”. Because of the importance of such a test for TSE infectivity to the safety of plasma products, the method of this invention was described generally at the Blood Safety and Screening conference held in McClean, Va. on Feb. 23, 1998.